1. Field of the Invention
The present invention relates to a wafer boat for holding a plurality of semiconductor wafers in a processing chamber of a vertical heating-treating apparatus.
2. Description of Related Art
In the manufacturing of semiconductor devices, a vertical heating-treating apparatus is used to perform a heat-treating process, e.g., thermal oxidation or thermal diffusion, on semiconductor wafers. A plurality of the wafers are so treated all together in what is known as batch processing. To this end, a large number of wafers are held by a heat-treating boat in a stacked state as spaced apart from one another. The boat is placed in a processing chamber of the heat-treating apparatus so that the wafers are heat-treated in their stacked state.
One example of a vertical heat-treating apparatus having a wafer boat for holding a plurality of wafers in a processing chamber is disclosed in U.S. Pat. No. 5,316,472 to Niino, et al. The semiconductor wafer boat disclosed in U.S. Pat. No. 5,316,472 includes four columns fixed to upper and lower support plates. Each of the columns has a plurality of first grooves defined at regular intervals in the vertical direction, and a plurality of second grooves disposed alternately with respect to the first grooves. The wafers are received in the first grooves, whereby they are supported substantially parallel to each other by the boat. Ring plates are received in each of the second grooves to ensure the uniformity of the thickness of a film to be formed on each wafer. Each ring plate has an outer diameter larger than that of a wafer, and an inner diameter smaller than that of the wafer. The ring plates are spaced from each other to provide sufficient clearance for allowing the wafers to be transferred into and out of the boat between adjacent ring plates.
Meanwhile, Japanese Patent Publication No. 2000-49106 discloses a semiconductor wafer boat having a pillar that will not deform. The semiconductor wafer boat disclosed in Japanese Patent Publication No. 2000-49106 includes a pillar extending vertically for supporting the wafers horizontally as spaced from one another by a specified interval, and an engagement part unitary with the pillar for suspending the boat from a boat loader while an upper part of the pillar is supported.
However, such conventional wafer boats suffer from thermal deformation when used for a long time, particularly because the wafer processing is preformed at high temperatures. Such thermal deformation occurs primarily in the columns that extend in a vertical direction orthogonally to the wafers. In particular, the thermal deformation is pronounced at an upper portion of the boat where the process gas accumulates, in a portion of the boat from which the process gas is exhausted, or where a ring plate and a column meet. As a result, the wafer boat may crack or flake.
Furthermore, such a wafer boat generally comprises quartz. Therefore, it is costly to replace the boat with a new one whenever thermal deformation occurs. Therefore, the tendency in the industry is to repair any deformed portion of the boat.
However, the columns of the wafer boat may be twisted during repair work such as the replacing of an old, deformed ring plate. A twisted column prevents the semiconductor wafers from being uniformly heat-treated. In addition, even if only a portion of the wafer boat is thermally deformed, the entire boat must often be replaced because the boat is formed as one body. Therefore, thermal deformation of a wafer boat gives rise to increased maintenance costs and, thus, increases the cost associated with manufacturing the semiconductor devices. Furthermore, the larger the wafer boat, the more the thermal deformation adversely affects the ability of the boat to facilitate a uniform heat treatment of the semiconductor wafers.
One object of the present invention is to provide a semiconductor wafer boat, and a semiconductor wafer processing apparatus comprising the same, by which batch after batch of semiconductor wafers can be heated uniformly.
Another object of the present invention is to provide a wafer boat, that is easy to maintain and repair.
A further object of the present invention is to provide a wafer boat that helps minimize the maintenance costs associated with operating a semiconductor wafer processing apparatus.
In order to achieve the above objects, the present invention provides a semiconductor wafer heat-treating boat that includes a plurality of stacked boat parts which are freely coupled to one another such that each of the boat parts is replaceable independently of the other boat parts.
The boat includes three types of such boat parts. Each of the boat parts includes a vertically extending wafer support having a plurality of vertically spaced apart support surfaces for use in supporting semiconductor wafers as vertically spaced from one another. The vertically extending wafer support has an upper and lower end portions, at least one of which is a free end defining half of a joint by which the boat part can be freely coupled to another boat part. A first type of this boat part includes an upper support plate and a plurality of first columns having upper and lower end portions. The upper end portions of the first column are joined with the upper support plate. A second type of boat part includes a plurality of second columns having upper and lower end portions. The upper end portions of the columns of a second boat part are coupled with the lower end portions of the first columns to form a first joint. The third type of boat part includes a lower support plate and a plurality of third columns having upper and lower end portions. The upper end portions of the third columns are coupled with the lower end portions of the columns of a second boat part to form a second joint. The lower end portions of the third columns are joined with the lower support plate.
Each of the joints may be made up of complementary convexo-concave end portions (one side convex, the other concave) of the first and second columns. Alternatively, the first and second columns may have an opening and a protrusion, respectively, at the end portions thereof. In this case, the opening has a shape suitable for producing a friction fit such that the protrusion is received in a snug manner.
Each of the first to third columns has a plurality of grooves extending perpendicular to the longitudinal axis of the column. The grooves are spaced from each other in the longitudinal direction of the column. The wafers may be received directly in the grooves. Alternatively, ring plates may be received in corresponding grooves of the columns of the boat parts. In this case, a plurality of main supports extend upright from the upper surface of each ring plate, and a plurality of protrusions extend from the main supports in a direction perpendicular thereto to substantially support a semiconductor wafer.
Because the heat-treating boat of the present invention has discrete separable boat parts, any part of the heat-treating boat in which thermal deformation occurs can be replaced. Thus, the boat is easy to maintain and repair. Also, the overall maintenance costs associated with the heating-treating apparatus are kept to a minimum. Also, repairing the heat-treating wafer boat is not likely to deform any parts of the boat. Accordingly, the semiconductor wafers will be uniformly heat-treated and thus, high quality semiconductor devices can be manufactured.